cant burn with nero anymore

ok heres what's happning i have burned movies before useing nero and now i cant it will transcode or something like that then it wont burn why is that... my dvd says its a multi recorder but i have been useing dvd - and it says on the side of the burner dvd+ but i have got movies to burn before on the disc.... all the videos are AVI so what am i doing worng please help

thanks ... for bareing with me here not verry good at this stuff... i am still haveing trobble do u have msn can u help me throught there..it would be verry much appreacheaded, its like 11.33 here is canada